linux-kernel - Re: [PATCH 1/2] futex: mark futex_detect

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Date:   Mon, 25 Oct 2021 15:52:04 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Marco Elver <elver@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        Russell King <linux@...linux.org.uk>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Darren Hart <dvhart@...radead.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] futex: mark futex_detect_cmpxchg() as 'noinline'

On Thu, Jul 22, 2021 at 10:05 PM Nathan Chancellor <nathan@...nel.org> wrote:
> On Sat, Dec 12, 2020 at 09:01:34PM +0100, Thomas Gleixner wrote:
> > --- a/arch/arm/Kconfig
> > +++ b/arch/arm/Kconfig
> > @@ -86,6 +86,7 @@ config ARM
> >       select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL
> >       select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG
> >       select HAVE_FUNCTION_TRACER if !XIP_KERNEL
> > +     select HAVE_FUTEX_CMPXCHG if FUTEX
> >       select HAVE_GCC_PLUGINS
> >       select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7)
> >       select HAVE_IDE if PCI || ISA || PCMCIA
>
> Did this ever get sent along as a formal patch? I just ran into another
> issue that seems to be similar to the one Arnd sent the initial patch in
> this thread for and it is resolved by this change.

Nick sent this patch in September, and Russell applied it as commit
9d417cbe36ee ("ARM: 9122/1: select HAVE_FUTEX_CMPXCHG").
This addresses the problem for arm, but I think we should really
just remove HAVE_FUTEX_CMPXCHG entirely and require it to
be there for SMP.

I have a patch for that, but that needs a separate fix for sparc32,
which I think nobody is interested in working on. I can post it anyway
to get discussion moving again.

         Arnd